Sidelink drx and standalone sidelink beam failure detection and recovery

ABSTRACT

Certain aspects of the present disclosure provide techniques for standalone sidelink beam failure recovery. In certain aspects, a method performed by a first user equipment may generally include communicating, while operating in a sidelink discontinuous reception (DRX) mode, with a second UE on a first communications link between the first UE and the second UE; transmitting, during an awake state of the sidelink DRX mode, at least one beam failure detection reference signal of a plurality of beam failure detection reference signals associated with the first communications link, wherein a periodicity of the awake state of the sidelink DRX mode is based on a periodicity for transmitting the plurality of beam failure detection reference signals; and detecting that the first communications link between the first UE and the second UE has failed based on the at least one beam failure detection reference signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of and priority to U.S. ProvisionalApplication No. 63/038,513, filed Jun. 12, 2020, which is herebyassigned to the assignee hereof and hereby expressly incorporated byreference herein in its entirety as if fully set forth below and for allapplicable purposes.

INTRODUCTION Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for sidelink discontinuous reception(DRX) and standalone sidelink beam failure detection and recovery.

DESCRIPTION OF RELATED ART

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,broadcasts, etc. These wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power, etc.). Examples of such multiple-access systems include3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)systems, LTE Advanced (LTE-A) systems, code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems, to name a few.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. New radio (e.g., 5G NR) is an exampleof an emerging telecommunication standard. NR is a set of enhancementsto the LTE mobile standard promulgated by 3GPP. NR is designed to bettersupport mobile broadband Internet access by improving spectralefficiency, lowering costs, improving services, making use of newspectrum, and better integrating with other open standards using OFDMAwith a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL).To these ends, NR supports beamforming, multiple-input multiple-output(MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in NR and LTEtechnology. Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedstandalone sidelink beam failure recovery.

Certain aspects of the subject matter described in this disclosure canbe implemented in a method for wireless communication by a first userequipment (UE). The method generally includes communicating, whileoperating in a sidelink discontinuous reception (DRX) mode, with asecond UE on a first communications link between the first UE and thesecond UE; transmitting, during an awake state of the sidelink DRX mode,at least one beam failure detection reference signal of a plurality ofbeam failure detection reference signals associated with the firstcommunications link, wherein a periodicity of the awake state of thesidelink DRX mode is based on a periodicity for transmitting theplurality of beam failure detection reference signals; and detectingthat the first communications link between the first UE and the secondUE has failed based on the at least one beam failure detection referencesignal.

Certain aspects of the subject matter described in this disclosure canbe implemented in an apparatus for wireless communications by a firstuser equipment (UE). The apparatus includes a memory comprisingexecutable instructions and one or more processors configured to executethe executable instructions and cause the apparatus to communicate,while operating in a sidelink discontinuous reception (DRX) mode, with asecond UE on a first communications link between the first UE and thesecond UE; transmit, during an awake state of the sidelink DRX mode, atleast one beam failure detection reference signal of a plurality of beamfailure detection reference signals associated with the firstcommunications link, wherein a periodicity of the awake state of thesidelink DRX mode is based on a periodicity for transmitting theplurality of beam failure detection reference signals; and detectingthat the first communications link between the first UE and the secondUE has failed based on the at least one beam failure detection referencesignal. The apparatus may also include a memory coupled with the atleast one processor.

Certain aspects of the subject matter described in this disclosure canbe implemented in an apparatus for wireless communications by a firstuser equipment (UE). The apparatus generally includes means forcommunicating, while operating in a sidelink discontinuous reception(DRX) mode, with a second UE on a first communications link between thefirst UE and the second UE; means for transmitting, during an awakestate of the sidelink DRX mode, at least one beam failure detectionreference signal of a plurality of beam failure detection referencesignals associated with the first communications link, wherein aperiodicity of the awake state of the sidelink DRX mode is based on aperiodicity for transmitting the plurality of beam failure detectionreference signals; and means for detecting that the first communicationslink between the first UE and the second UE has failed based on the atleast one beam failure detection reference signal.

Certain aspects of the subject matter described in this disclosure canbe implemented in a non-transitory computer-readable medium for wirelesscommunications by a first user equipment (UE). The non-transitorycomputer-readable medium includes executable instructions that, whenexecuted by one or more processors of an apparatus, cause the apparatusto communicate, while operating in a sidelink discontinuous reception(DRX) mode, with a second UE on a first communications link between thefirst UE and the second UE; transmit, during an awake state of thesidelink DRX mode, at least one beam failure detection reference signalof a plurality of beam failure detection reference signals associatedwith the first communications link, wherein a periodicity of the awakestate of the sidelink DRX mode is based on a periodicity fortransmitting the plurality of beam failure detection reference signals;and detecting that the first communications link between the first UEand the second UE has failed based on the at least one beam failuredetection reference signal.

Certain aspects of the subject matter described in this disclosure canbe implemented in a method for wireless communication by a second userequipment (UE). The method generally includes communicating, during anawake state of a sidelink discontinuous reception (DRX) mode, with afirst UE on a first communications link between the first UE and thesecond UE, wherein a periodicity of the awake state of the sidelink DRXmode is based on a periodicity for receiving a plurality of beam failuredetection reference signals associated with the first communicationslink; and monitoring, during the awake state of the sidelink DRX mode,for the plurality of beam failure detection reference signals accordingto the periodicity for receiving the plurality of beam failure detectionreference signals.

Certain aspects of the subject matter described in this disclosure canbe implemented in an apparatus for wireless communications by a seconduser equipment (UE). The apparatus includes a memory comprisingexecutable instructions and one or more processors configured to executethe executable instructions and cause the apparatus to communicate,during an awake state of a sidelink discontinuous reception (DRX) mode,with a first UE on a first communications link between the first UE andthe second UE, wherein a periodicity of the awake state of the sidelinkDRX mode is based on a periodicity for receiving a plurality of beamfailure detection reference signals associated with the firstcommunications link; and monitor, during the awake state of the sidelinkDRX mode, for the plurality of beam failure detection reference signalsaccording to the periodicity for receiving the plurality of beam failuredetection reference signals. The apparatus may also include a memorycoupled with the at least one processor.

Certain aspects of the subject matter described in this disclosure canbe implemented in an apparatus for wireless communications by a seconduser equipment (UE). The apparatus generally includes means forcommunicating, during an awake state of a sidelink discontinuousreception (DRX) mode, with a first UE on a first communications linkbetween the first UE and the second UE, wherein a periodicity of theawake state of the sidelink DRX mode is based on a periodicity forreceiving a plurality of beam failure detection reference signalsassociated with the first communications link; and means for monitoring,during the awake state of the sidelink DRX mode, for the plurality ofbeam failure detection reference signals according to the periodicityfor receiving the plurality of beam failure detection reference signals.

Certain aspects of the subject matter described in this disclosure canbe implemented in a non-transitory computer-readable medium for wirelesscommunications by a second user equipment (UE). The non-transitorycomputer-readable medium includes executable instructions that, whenexecuted by one or more processors of an apparatus, cause the apparatusto communicate, during an awake state of a sidelink discontinuousreception (DRX) mode, with a first UE on a first communications linkbetween the first UE and the second UE, wherein a periodicity of theawake state of the sidelink DRX mode is based on a periodicity forreceiving a plurality of beam failure detection reference signalsassociated with the first communications link; and monitor, during theawake state of the sidelink DRX mode, for the plurality of beam failuredetection reference signals according to the periodicity for receivingthe plurality of beam failure detection reference signals.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein, both their organization and method ofoperation, together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purposesof illustration and description, and not as a definition of the limitsof the claims.

While aspects and embodiments are described in this application byillustration to some examples, those skilled in the art will understandthat additional implementations and use cases may come about in manydifferent arrangements and scenarios. Innovations described herein maybe implemented across many differing platform types, devices, systems,shapes, sizes, packaging arrangements. For example, embodiments and/oruses may come about via integrated chip embodiments and othernon-module-component based devices (e.g., end-user devices, vehicles,communication devices, computing devices, industrial equipment,retail/purchasing devices, medical devices, AI-enabled devices, etc.).While some examples may or may not be specifically directed to use casesor applications, a wide assortment of applicability of describedinnovations may occur. Implementations may range in spectrum fromchip-level or modular components to non-modular, non-chip-levelimplementations and further to aggregate, distributed, or OEM devices orsystems incorporating one or more aspects of the described innovations.In some practical settings, devices incorporating described aspects andfeatures may also necessarily include additional components and featuresfor implementation and practice of claimed and described embodiments.For example, transmission and reception of wireless signals necessarilyincludes a number of components for analog and digital purposes (e.g.,hardware components including antenna, RF-chains, power amplifiers,modulators, buffer, processor(s), interleaver, adders/summers, etc.). Itis intended that innovations described herein may be practiced in a widevariety of devices, chip-level components, systems, distributedarrangements, end-user devices, etc. of varying sizes, shapes, andconstitution.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the drawings. It is to be noted, however, thatthe appended drawings illustrate only certain typical aspects of thisdisclosure and are therefore not to be considered limiting of its scope,for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an example wirelesscommunication network, in accordance with certain aspects of the presentdisclosure.

FIG. 2 is a block diagram conceptually illustrating a design of anexample a base station (BS) and user equipment (UE), in accordance withcertain aspects of the present disclosure.

FIG. 3 is an example frame format for certain wireless communicationsystems (e.g., new radio (NR)), in accordance with certain aspects ofthe present disclosure.

FIG. 4A and FIG. 4B show diagrammatic representations of example vehicleto everything (V2X) systems, in accordance with certain aspects of thepresent disclosure.

FIG. 5 is a call flow diagram illustrating example resource allocationfor sidelink transmission, in accordance with certain aspects of thepresent disclosure.

FIG. 6 is a call flow diagram illustrating example autonomous resourceselection for sidelink transmission, in accordance with certain aspectsof the present disclosure.

FIG. 7 is a flow diagram illustrating example operations for wirelesscommunication by a first UE, in accordance with certain aspects of thepresent disclosure.

FIG. 8 is a flow diagram illustrating example operations for wirelesscommunication by a second UE, in accordance with certain aspects of thepresent disclosure.

FIGS. 9-10 depict aspects of example communications devices, inaccordance with certain aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer readable mediums for sidelink discontinuousreception (DRX) and standalone sidelink beam failure detection andrecovery. For example, in some cases, two user equipments in a wirelesscommunication network may communicate with each other using a sidelinkcommunication link/channel via one or more transmission beams and one ormore reception beams. During sidelink communication, the UEs may alsooperate according to a DRX mode that allows each UE to transition to asleep state to conserve power. However, operating in the sleep state ofthe DRX mode may interfere with resources for transmitting and receivingbeam failure detection reference signals used to detect a failure of thesidelink communication link, which may result in a failure of thesidelink communication link not being detected. As a consequence, anundetected sidelink communication link failure may lead to unnecessarytransmissions that will ultimately fail to be received and, as aconsequence, wasted time and frequency resources in the wirelesscommunication network as well as power resources at the UEs.Additionally, because the sleep state of the DRX mode may be differentfor the two UEs, it may be difficult for these UEs to reestablish thesidelink communication link.

Accordingly, to avoid interference between the DRX mode and theresources for the beam failure detection reference signals, aspects ofthe present disclosure provide techniques for configuring a periodicityassociated with the DRX mode based on a periodicity associated with theresources for the beam failure detection reference signals. By basingthe periodicity of the DRX mode on the periodicity associated with theresources for beam failure detection reference signals, a likelihood ofinterference between the DRX mode and the resources for beam failuredetection reference signals may be reduced. As such, the likelihood ofmissing the detection of a failed sidelink communication link may alsobe reduced, which helps to avoid unnecessary transmission on a failedsidelink communication link (e.g., saving the time, frequency, and powerresources) and help to quickly and efficiently reestablish the failedsidelink communication link.

The following description provides examples of sidelink DRX andstandalone sidelink beam failure detection and recovery, and is notlimiting of the scope, applicability, or examples set forth in theclaims. Changes may be made in the function and arrangement of elementsdiscussed without departing from the scope of the disclosure. Variousexamples may omit, substitute, or add various procedures or componentsas appropriate. For instance, the methods described may be performed inan order different from that described, and various steps may be added,omitted, or combined. Also, features described with respect to someexamples may be combined in some other examples. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, the scope of thedisclosure is intended to cover such an apparatus or method which ispracticed using other structure, functionality, or structure andfunctionality in addition to, or other than, the various aspects of thedisclosure set forth herein. It should be understood that any aspect ofthe disclosure disclosed herein may be embodied by one or more elementsof a claim. The word “exemplary” is used herein to mean “serving as anexample, instance, or illustration.” Any aspect described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a subcarrier, afrequency channel, a tone, a subband, etc. Each frequency may support asingle RAT in a given geographic area in order to avoid interferencebetween wireless networks of different RATs.

The techniques described herein may be used for various wirelessnetworks and radio technologies. While aspects may be described hereinusing terminology commonly associated with 3G, 4G, and/or new radio(e.g., 5G NR) wireless technologies, aspects of the present disclosurecan be applied in other generation-based communication systems.

NR access may support various wireless communication services, such asenhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHzor beyond), millimeter wave (mmW) targeting high carrier frequency(e.g., e.g., 24 GHz to 53 GHz or beyond), massive machine typecommunications MTC (mMTC) targeting non-backward compatible MTCtechniques, and/or mission critical targeting ultra-reliable low-latencycommunications (URLLC). These services may include latency andreliability requirements. These services may also have differenttransmission time intervals (TTI) to meet respective quality of service(QoS) requirements. In addition, these services may co-exist in the samesubframe. NR supports beamforming and beam direction may be dynamicallyconfigured. MIMO transmissions with precoding may also be supported.MIMO configurations in the DL may support up to 8 transmit antennas withmulti-layer DL transmissions up to 8 streams and up to 2 streams per UE.Multi-layer transmissions with up to 2 streams per UE may be supported.Aggregation of multiple cells may be supported with up to 8 servingcells.

FIG. 1 illustrates an example wireless communication network 100 inwhich aspects of the present disclosure may be performed. For example,the wireless communication network 100 may be an NR system (e.g., a 5GNR network). As shown in FIG. 1, the wireless communication network 100may be in communication with a core network 132. The core network 132may be in communication with one or more B Ss 110 and/or UEs 120 in thewireless communication network 100 via one or more interfaces.

According to certain aspects, the UEs 120 may be configured forstandalone beam failure recovery as described herein. For example, asshown, the UEs 120 a and 120 b may include a sidelink beam failurerecovery (BFR) module 122 a and 122 b, respectively, that may beconfigured for sidelink discontinuous reception (DRX) and standalonesidelink beam failure detection and recovery as described herein, inaccordance with aspects of the present disclosure. For example, in somecases, the sidelink BFR module 122 a and 122 b may be configured toperform the operations illustrated in one or more of FIG. 7 or FIG. 8,as well as other operations disclosed herein for sidelink DRX andstandalone sidelink beam failure detection and recovery.

As illustrated in FIG. 1, the wireless communication network 100 mayinclude a number of BSs 110 a-z (each also individually referred toherein as BS 110 or collectively as BSs 110) and other network entities.A BS 110 may provide communication coverage for a particular geographicarea, sometimes referred to as a “cell”, which may be stationary or maymove according to the location of a mobile BS 110. In some examples, theBSs 110 may be interconnected to one another and/or to one or more otherBSs or network nodes (not shown) in wireless communication network 100through various types of backhaul interfaces (e.g., a direct physicalconnection, a wireless connection, a virtual network, or the like) usingany suitable transport network. In the example shown in FIG. 1, the BSs110 a, 110 b and 110 c may be macro BSs for the macro cells 102 a, 102 band 102 c, respectively. The BS 110 x may be a pico BS for a pico cell102 x. The BSs 110 y and 110 z may be femto BSs for the femto cells 102y and 102 z, respectively. ABS may support one or multiple cells.

The BSs 110 communicate with UEs 120 a-y (each also individuallyreferred to herein as UE 120 or collectively as UEs 120) in the wirelesscommunication network 100. The UEs 120 (e.g., 120 x, 120 y, etc.) may bedispersed throughout the wireless communication network 100, and each UE120 may be stationary or mobile. Wireless communication network 100 mayalso include relay stations (e.g., relay station 110 r), also referredto as relays or the like, that receive a transmission of data and/orother information from an upstream station (e.g., a BS 110 a or a UE 120r) and sends a transmission of the data and/or other information to adownstream station (e.g., a UE 120 or a BS 110), or that relaystransmissions between UEs 120, to facilitate communication betweendevices.

A network controller 130 may be in communication with a set of BSs 110and provide coordination and control for these BSs 110 (e.g., via abackhaul). In aspects, the network controller 130 may be incommunication with a core network 132 (e.g., a 5G Core Network (5GC)),which provides various network functions such as Access and MobilityManagement, Session Management, User Plane Function, Policy ControlFunction, Authentication Server Function, Unified Data Management,Application Function, Network Exposure Function, Network RepositoryFunction, Network Slice Selection Function, etc.

FIG. 2 illustrates example components of BS 110 a and UE 202, which maybe used to implement aspects of the present disclosure. UE 202 maycomprise UE 120 a, 120 b, or UE 120 c of FIG. 1

At the BS 110 a, a transmit processor 220 may receive data from a datasource 212 and control information from a controller/processor 240. Thecontrol information may be for the physical broadcast channel (PBCH),physical control format indicator channel (PCFICH), physical hybrid ARQindicator channel (PHICH), physical downlink control channel (PDCCH),group common PDCCH (GC PDCCH), etc. The data may be for the physicaldownlink shared channel (PDSCH), etc. A medium access control(MAC)-control element (MAC-CE) is a MAC layer communication structurethat may be used for control command exchange between wireless nodes.The MAC-CE may be carried in a shared channel such as a physicaldownlink shared channel (PDSCH), a physical uplink shared channel(PUSCH), or a physical sidelink shared channel (PSSCH).

The processor 220 may process (e.g., encode and symbol map) the data andcontrol information to obtain data symbols and control symbols,respectively. The transmit processor 220 may also generate referencesymbols, such as for the primary synchronization signal (PSS), secondarysynchronization signal (SSS), PBCH demodulation reference signal (DMRS),and channel state information reference signal (CSI-RS). A transmit (TX)multiple-input multiple-output (MIMO) processor 230 may perform spatialprocessing (e.g., precoding) on the data symbols, the control symbols,and/or the reference symbols, if applicable, and may provide outputsymbol streams to the modulators (MODs) in transceivers 232 a-232 t.Each modulator in transceivers 232 a-232 t may process a respectiveoutput symbol stream (e.g., for OFDM, etc.) to obtain an output samplestream. Each modulator may further process (e.g., convert to analog,amplify, filter, and upconvert) the output sample stream to obtain adownlink signal. Downlink signals from the modulators in transceivers232 a-232 t may be transmitted via the antennas 234 a-234 t,respectively.

At the UE 202, the antennas 252 a-252 r may receive the downlink signalsfrom the BS 110 a and may provide received signals to the demodulators(DEMODs) in transceivers 254 a-254 r, respectively. Each demodulator intransceivers 254 a-254 r may condition (e.g., filter, amplify,downconvert, and digitize) a respective received signal to obtain inputsamples. Each demodulator may further process the input samples (e.g.,for OFDM, etc.) to obtain received symbols. A MIMO detector 256 mayobtain received symbols from all the demodulators in transceivers 254a-254 r, perform MIMO detection on the received symbols if applicable,and provide detected symbols. A receive processor 258 may process (e.g.,demodulate, deinterleave, and decode) the detected symbols, providedecoded data for the UE 202 to a data sink 260, and provide decodedcontrol information to a controller/processor 280.

On the uplink, at UE 202, a transmit processor 264 may receive andprocess data (e.g., for the physical uplink shared channel (PUSCH)) froma data source 262 and control information (e.g., for the physical uplinkcontrol channel (PUCCH) from the controller/processor 280. The transmitprocessor 264 may also generate reference symbols for a reference signal(e.g., for the sounding reference signal (SRS)). The symbols from thetransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by the modulators in transceivers 254a-254 r (e.g., for SC-FDM, etc.), and transmitted to the BS 110 a. Atthe BS 110 a, the uplink signals from the UE 202 may be received by theantennas 234, processed by the demodulators 232, detected by a MIMOdetector 236 if applicable, and further processed by a receive processor238 to obtain decoded data and control information sent by the UE 202.The receive processor 238 may provide the decoded data to a data sink239 and the decoded control information to the controller/processor 240.

The memories 242 and 282 may store data and program codes for BS 110 aand UE 202, respectively. A scheduler 244 may schedule UEs for datatransmission on the downlink and/or uplink.

Antennas 252, processors 266, 258, 264, and/or controller/processor 280of the UE 202 and/or antennas 234, processors 220, 230, 238, and/orcontroller/processor 240 of the BS 110 a may be used to perform thevarious techniques and methods described herein. For example, shown inFIG. 2, the controller/processor 280 of the UE 202 includes a sidelinkbeam failure recovery (BFR) module 281 that may be configured forsidelink discontinuous reception (DRX) and standalone sidelink beamfailure detection and recovery, according to aspects described herein.For example, in some cases, the sidelink BFR module 281 may beconfigured to perform the operations illustrated in one or more of FIG.7 or FIG. 8, as well as other operations described herein for standalonebeam failure recovery. Although shown at the controller/processor, othercomponents of the UE 202 and BS 110 a may be used to perform theoperations described herein.

NR may utilize orthogonal frequency division multiplexing (OFDM) with acyclic prefix (CP) on the uplink and downlink. NR may supporthalf-duplex operation using time division duplexing (TDD). OFDM andsingle-carrier frequency division multiplexing (SC-FDM) partition thesystem bandwidth into multiple orthogonal subcarriers, which are alsocommonly referred to as tones, bins, etc. Each subcarrier may bemodulated with data. Modulation symbols may be sent in the frequencydomain with OFDM and in the time domain with SC-FDM. The spacing betweenadjacent subcarriers may be fixed, and the total number of subcarriersmay be dependent on the system bandwidth. The minimum resourceallocation, called a resource block (RB), may be 12 consecutivesubcarriers. The system bandwidth may also be partitioned into subbands.For example, a subband may cover multiple RBs. NR may support a basesubcarrier spacing (SCS) of 15 KHz and other SCS may be defined withrespect to the base SCS (e.g., 30 kHz, 60 kHz, 120 kHz, 240 kHz, etc.).

FIG. 3 is a diagram showing an example of a frame format 300 for NR. Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames. Each radio frame may have apredetermined duration (e.g., 10 ms) and may be partitioned into 10subframes, each of 1 ms, with indices of 0 through 9. Each subframe mayinclude a variable number of slots (e.g., 1, 2, 4, 8, 16, . . . slots)depending on the SCS. Each slot may include a variable number of symbolperiods (e.g., 7, 12, or 14 symbols) depending on the SCS. The symbolperiods in each slot may be assigned indices. A mini-slot, which may bereferred to as a sub-slot structure, refers to a transmit time intervalhaving a duration less than a slot (e.g., 2, 3, or 4 symbols). Eachsymbol in a slot may indicate a link direction (e.g., DL, UL, orflexible) for data transmission and the link direction for each subframemay be dynamically switched. The link directions may be based on theslot format. Each slot may include DL/UL data as well as DL/UL controlinformation.

In NR, a synchronization signal block (SSB) is transmitted. In certainaspects, SSBs may be transmitted in a burst where each SSB in the burstcorresponds to a different beam direction for UE-side beam management(e.g., including beam selection and/or beam refinement). The SSBincludes a PSS, a SSS, and a two symbol PBCH. The SSB can be transmittedin a fixed slot location, such as the symbols 0-3 as shown in FIG. 3.The PSS and SSS may be used by UEs for cell search and acquisition. ThePSS may provide half-frame timing, the SS may provide the CP length andframe timing. The PSS and SSS may provide the cell identity. The PBCHcarries some basic system information, such as downlink systembandwidth, timing information within radio frame, SS burst setperiodicity, system frame number, etc. The SSBs may be organized into SSbursts to support beam sweeping. Further system information such as,remaining minimum system information (RMSI), system information blocks(SIBs), other system information (OSI) can be transmitted on a physicaldownlink shared channel (PDSCH) in certain subframes. The SSB can betransmitted up to sixty-four times, for example, with up to sixty-fourdifferent beam directions for mmWave. The multiple transmissions of theSSB are referred to as a SS burst set. SSBs in an SS burst set may betransmitted in the same frequency region, while SSBs in different SSbursts sets can be transmitted at different frequency regions.

In some examples, the communication between the UEs 120 and BSs 110 isreferred to as the access link. The access link may be provided via a Uuinterface. Communication between devices, such as UEs, may be referredas the sidelink.

In some examples, two or more subordinate entities (e.g., UEs 120) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE 120 a) to anothersubordinate entity (e.g., another UE 120) without relaying thatcommunication through the scheduling entity (e.g., UE 120 or BS 110),even though the scheduling entity may be utilized for scheduling and/orcontrol purposes. In some examples, the sidelink signals may becommunicated using a licensed spectrum (unlike wireless local areanetworks, which typically use an unlicensed spectrum). One example ofsidelink communication is PC5, for example, as used in V2V, LTE, and/orNR.

Various sidelink channels may be used for sidelink communications,including a physical sidelink discovery channel (PSDCH), a physicalsidelink control channel (PSCCH), a physical sidelink shared channel(PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH maycarry discovery expressions that enable proximal devices to discovereach other. The PSCCH may carry control signaling such as sidelinkresource configurations and other parameters used for datatransmissions, and the PSSCH may carry the data transmissions. The PSFCHmay carry feedback such as CSI related to a sidelink channel quality.

FIG. 4A and FIG. 4B show diagrammatic representations of example V2Xsystems, in accordance with some aspects of the present disclosure. Forexample, the vehicles shown in FIG. 4A and FIG. 4B may communicate viasidelink channels and may perform sidelink CSI reporting as describedherein.

The V2X systems, provided in FIG. 4A and FIG. 4B provide twocomplementary transmission modes. A first transmission mode, shown byway of example in FIG. 4A, involves direct communications (for example,also referred to as sidelink communications) between participants inproximity to one another in a local area. A second transmission mode,shown by way of example in FIG. 4B, involves network communicationsthrough a network, which may be implemented over a Uu interface (forexample, a wireless communication interface between a radio accessnetwork (RAN) and a UE).

Referring to FIG. 4A, a V2X system 400 (for example, including vehicleto vehicle (V2V) communications) is illustrated with two vehicles 402,404. The first transmission mode allows for direct communication betweendifferent participants in a given geographic location. As illustrated, avehicle can have a wireless communication link 406 with an individual(V2P) (for example, via a UE) through a PC5 interface. Communicationsbetween the vehicles 402 and 404 may also occur through a PC5 interface408. In a like manner, communication may occur from a vehicle 402 toother highway components (for example, highway component 410), such as atraffic signal or sign (V2I) through a PC5 interface 412. With respectto each communication link illustrated in FIG. 4A, two-way communicationmay take place between elements, therefore each element may be atransmitter and a receiver of information. The V2X system 400 may be aself-managed system implemented without assistance from a networkentity. A self-managed system may enable improved spectral efficiency,reduced cost, and increased reliability as network service interruptionsdo not occur during handover operations for moving vehicles. The V2Xsystem may be configured to operate in a licensed or unlicensedspectrum, thus any vehicle with an equipped system may access a commonfrequency and share information. Such harmonized/common spectrumoperations allow for safe and reliable operation.

FIG. 4B shows a V2X system 450 for communication between a vehicle 452and a vehicle 454 through a network entity 456. These networkcommunications may occur through discrete nodes, such as a BS (e.g., theBS 110 a), that sends and receives information to and from (for example,relays information between) vehicles 452, 454. The networkcommunications through vehicle to network (V2N) links 458 and 410 may beused, for example, for long range communications between vehicles, suchas for communicating the presence of a car accident a distance aheadalong a road or highway. Other types of communications may be sent bythe wireless node to vehicles, such as traffic flow conditions, roadhazard warnings, environmental/weather reports, and service stationavailability, among other examples. Such data can be obtained fromcloud-based sharing services.

Roadside units (RSUs) may be utilized. An RSU may be used for V2Icommunications. In some examples, an RSU may act as a forwarding node toextend coverage for a UE. In some examples, an RSU may be co-locatedwith a BS or may be standalone. RSUs can have different classifications.For example, RSUs can be classified into UE-type RSUs and MicroNodeB-type RSUs. Micro NB-type RSUs have similar functionality as theMacro eNB/gNB. The Micro NB-type RSUs can utilize the Uu interface.UE-type RSUs can be used for meeting tight quality-of-service (QoS)requirements by minimizing collisions and improving reliability. UE-typeRSUs may use centralized resource allocation mechanisms to allow forefficient resource utilization. Critical information (e.g., such astraffic conditions, weather conditions, congestion statistics, sensordata, etc.) can be broadcast to UEs in the coverage area. Relays canre-broadcasts critical information received from some UEs. UE-type RSUsmay be a reliable synchronization source.

As noted above, certain devices may communicate with each other on asidelink channel. In some cases, such communication may be performedaccording to one or more resource allocation modes.

For example, in one resource allocation mode (e.g., gNB-assistedsidelink resource allocation Mode 1), a serving gNB allocates sidelinkresources for sidelink transmission. As shown in FIG. 5, the UE 502 maysend a sidelink buffer status report (SL-BSR) at 508 to the serving gNB506 (e.g., via Uu). The SL-BSR provides the serving gNB 506 withinformation about sidelink data volume of logical channel identifiers(LDICs) to each destination ID. The gNB 506 receives the SL-BSR andprovides a SL grant, at 510, to the UE 502 allocated resources forsidelink transmission from the transmitting UE 502 to the receiving UE504. At 512, the UE 502 sends a SL transmission (e.g., via PC5) to theUE 504 using the granted resources.

In another resource allocation mode (e.g., standalone sidelink resourceallocation Mode 2), the UEs may autonomously select sidelink resources(e.g., time and/or frequency resources) without assistance from the gNB.For example, as shown in FIG. 6, at 606, a transmitting UE 602autonomously selects and reserves resources for sidelink transmission.At 608, the transmitting UE 602 sends a SL transmission to the receivingUE 604 using the autonomously selected resources (e.g., via PC5).

Introduction to mmWave Wireless Communications

In wireless communications, an electromagnetic spectrum is oftensubdivided into various classes, bands, channels, or other features. Thesubdivision is often provided based on wavelength and frequency, wherefrequency may also be referred to as a carrier, a subcarrier, afrequency channel, a tone, or a subband.

5G networks may utilize several frequency ranges, which in some casesare defined by a standard, such as the 3GPP standards. For example, 3GPPtechnical standard TS 38.101 currently defines Frequency Range 1 (FR1)as including 600 MHz-6 GHz, though specific uplink and downlinkallocations may fall outside of this general range. Thus, FR1 is oftenreferred to (interchangeably) as a “Sub-6 GHz” band.

Similarly, TS 38.101 currently defines Frequency Range 2 (FR2) asincluding 26-41 GHz, though again specific uplink and downlinkallocations may fall outside of this general range. FR2, is sometimesreferred to (interchangeably) as a “millimeter wave” (“mmW” or “mmWave”)band, despite being different from the extremely high frequency (EHF)band (30 GHz-300 GHz) that is identified by the InternationalTelecommunications Union (ITU) as a “millimeter wave” band becausewavelengths at these frequencies are between 1 millimeter and 10millimeters.

Communications using mmWave/near mmWave radio frequency band (e.g., 3GHz-300 GHz) may have higher path loss and a shorter range compared tolower frequency communications. Accordingly, a mmWave base station(e.g., BS 110 a) may utilize beamforming with a UE (e.g., UE 120 a or120 b) to improve path loss and range. To do so, base station and the UEmay each include a plurality of antennas, such as antenna elements,antenna panels, and/or antenna arrays to facilitate the beamforming.

In some cases, base station may transmit a beamformed signal to UE inone or more transmit directions. The UE may receive the beamformedsignal from the base station in one or more receive directions. The UEmay also transmit a beamformed signal to the base station in one or moretransmit directions. The base station may receive the beamformed signalfrom the UE in one or more receive directions. The base station and theUE may then perform beam training to determine the best receive andtransmit directions for each of the base station and the UE. Notably,the transmit and receive directions for the base station may or may notbe the same. Similarly, the transmit and receive directions for the UEmay or may not be the same. Additionally, similar techniques for mmWavebeamforming may be used between two UEs for communication on thesidelink.

Example Sidelink DRX and Standalone Sidelink Beam Failure Detection andRecovery

As noted above, two or more UEs (e.g., UE 120 a and UE 120 b) maycommunicate with each other via a sidelink connection/channel using aparticular resource allocation mode. In some cases, such resourceallocation mode may comprise a standalone sidelink resource allocationmode (e.g., Mode 2), in which the UEs may autonomously select sidelinkresources (e.g., time and/or frequency resources) for communicationwithout the assistance of a base station, as illustrated in FIG. 6.

In many cases, the UEs may use a millimeter wave (mmWave) frequency whencommunicating via a sidelink connection. The sidelink connection, whenusing mmWave, may be composed of one or more directional beams (e.g.,transmission and reception beams) at each UE, which may be generatedusing beamforming. For example, in some cases, the UE 120 a may transmitinformation to the UE 120 b on the sidelink using a first transmission(Tx) beam and the UE 120 b may receive information from the UE 120 ausing a first reception (Rx) beam. Likewise, the UE 120 b may transmitinformation to the UE 120 a on the sidelink using a second Tx beam andthe UE 120 a may receive the information from the UE 120 b using asecond Rx beam. In some cases, the first Tx beam of the UE 120 a and thefirst Rx beam of the UE 120 b may be known as a beam pair link.

In some cases, each UE may be configured with resources for transmittingbeam failure detection reference signals for detecting a beam failure inthe beam pair link/sidelink connection. In some cases, the beam failuredetection reference signals may comprise sidelink reference signals suchas a sidelink channel state information reference signal (CSI-RS) and/ora sidelink synchronization signal block (SSB). A beam failure may occur,for example, when a first UE moves outside an area covered by theprevious Tx/Rx beams used for communication on the sidelink with asecond UE such that the second UE is not able receive signals from thefirst UE or vice versa. In this case, for example, the beam failure maybe detected, for example, when the first UE transmits a beam failuredetection reference signals using known resources but does not receive aresponse to the beam failure detection reference signals from the secondUE. In other cases, the beam failure may be inferred by the first UEwhen the UE receives connection request from the second UE on adifferent Tx/Rx beam than that used previously between the first UE andthe second UE.

In many cases, each UE may operate according to a discontinuousreception (DRX) mode associated with the sidelink connection. Forexample, the DRX mode allows a UE to periodically operate in an awakestate (e.g., an active mode) in which the UE may transmit or receivesignals and to periodically operate in a sleep state (e.g., a sleepmode) in which a modem of the UE remains idle and does not transmit orreceive signals, allowing the UE to conserve power when in the sleepstate.

When a beam failure is detected on the sidelink connection by either thefirst UE or the second UE, a sidelink beam failure recovery proceduremay be performed to recover connection between the first UE and thesecond UE. For example, in some cases, the first UE may transmit SSBsusing different transmission beams and may receive a random accesschannel (RACH) message from the second UE in response to the transmittedSSBs. The first UE may respond to the RACH message transmitted by thesecond UE with a RACH response message to reestablish the sidelinkconnection.

However, when each UE is operating in a DRX mode, the sleep state of theDRX mode may interference with the resources for transmitting the beamfailure detection reference signals. For example, in some cases, theresources for transmitting the beam failure detection reference signalsmay occur during the sleep state of the DRX mode, rendering the UEsunable to transmit the beam failure detection reference signals and,thus, to detect a beam failure on the sidelink. Accordingly, aspects ofthe present disclosure provide techniques for addressing these issueswith beam failure detection while operating in a DRX mode. In somecases, such techniques may involve configuring a periodicity of theawake state of the DRX mode based on a periodicity of the resources fortransmitting the plurality of beam failure detection reference signals.

FIG. 7 is a flow diagram illustrating example operations 700 forwireless communication for sidelink DRX and standalone sidelink beamfailure detection and recovery, in accordance with certain aspects ofthe present disclosure. The operations 700 may be performed, forexample, by a first sidelink (SL) device (e.g., the UE 120 a and/or theUE 120 b in the wireless communication network 100). The operations 700may be implemented as software components that are executed and run onone or more processors (e.g., controller/processor 280 of FIG. 2).Further, the transmission and reception of signals by the apparatus inoperations 700 may be enabled, for example, by one or more antennas(e.g., antennas 252 of FIG. 2). In certain aspects, the transmissionand/or reception of signals by the apparatus may be implemented via abus interface of one or more processors (e.g., controller/processor 280)obtaining and/or outputting signals.

The operations 700 may begin, at 702, by communicating, while operatingin a sidelink discontinuous reception (DRX) mode, with a second UE on afirst communications link between the first UE and the second UE.

At 704, the SL device transmits, during an awake state of the sidelinkDRX mode, at least one beam failure detection reference signal of aplurality of beam failure detection reference signals associated withthe first communications link, wherein a periodicity of the awake stateof the sidelink DRX mode is based on a periodicity for transmitting theplurality of beam failure detection reference signals.

At 706, the SL device detects that the first communications link betweenthe first UE and the second UE has failed based on the at least one beamfailure detection reference signal.

As noted above, a first UE (e.g., UE 120 a) may communicate, whileoperating in a sidelink DRX mode, with a second UE on a firstcommunications link between the first UE and the second UE. In somecases, the first communications link may comprise a sidelink between thefirst UE and the second UE. In some cases, communication on the sidelinkmay be performed according to a resource allocation mode in which theUEs may autonomously select sidelink resources (e.g., time and/orfrequency resources) for communication without the assistance of a basestation, such as a standalone sidelink resource allocation Mode 2.Additionally, as noted above, in some cases, communicating using thefirst communications link (e.g., sidelink) may involve using one or morebeamformed directional beams, such as a directional transmission beamand a direction reception beam. For example, in some cases, the first UEmay transmit information to the second UE on the first communicationslink using a first transmission beam and the second UE may receive theinformation using a first receive beam. In some cases, the firsttransmission beam and the first reception beam may be known as a beampair link.

In some cases, the first UE and the second UE may be configured withresources for transmitting beam failure detection reference signals,such as sidelink CSI-RSs and/or sidelink SSBs. In such cases, due topotential conflict between the resources for transmitting the beamfailure detection reference signals and a sleep state of the sidelinkDRX mode, a periodicity associated with the sidelink DRX mode may bebased on the resources for transmitting the beam failure detectionreference signals. For example, in some cases, a periodicity of an awakestate of the sidelink DRX mode may be based on a periodicity fortransmitting the plurality of beam failure detection reference signals.In other words, for example, the resources for transmitting the beamfailure detection reference signals may coincide with the awake state ofthe sidelink DRX mode, ensuring that the UE is awake and able totransmit/receive the beam failure detection reference signals during theconfigured resources.

Additionally, in some cases, if periodicity of the resources fortransmitting and receiving the plurality of beam failure detectionreference signals is adjusted, the periodicity of the awake state of theDRX mode may be adjusted. For example, the periodicity of the awakestate of the DRX mode may be increased if there is an increase in theperiodicity of the resources for transmitting and receiving theplurality of beam failure detection reference signals. Similarly, theperiodicity of the awake state of the DRX mode may be decreased if theperiodicity of the resource for transmitting and receiving the pluralityof beam failure detection reference signals is decreased.

Accordingly, during an awake state of the sidelink DRX mode, the firstUE may transmit at least one beam failure detection reference signal ofa plurality of beam failure detection reference signals associated withthe first communications link, for example, using the configuredresources for transmitting the beam failure detection reference signals.

Thereafter, in some cases, the first UE may detect that the firstcommunications link between the first UE and the second UE has failedbased on the at least one beam failure detection reference signal. Insome cases, the first UE may detect that the first communications linkbetween the first UE and the second UE has failed based on the first UEnot receiving, within a threshold period of time, a response messagefrom the second UE, responding to the at least one beam failuredetection reference signal. In some cases, the response message maycomprise an acknowledgement message.

In other cases, the first UE may receive a sidelink random accesschannel (RACH) message from the second UE in response to the at leastone beam failure detection reference signal (e.g., an SSB) and maydetect that the first communications link between the first UE and thesecond UE has failed based on the sidelink RACH message received fromthe second UE. For example, as noted above, the first UE and second UEmay communicate on the sidelink using a first transmission beam (e.g.,at the first UE) and a first reception beam (e.g., as the second UE).Accordingly, if the RACH message received from the second UE includes anindication of a transmission beam different from the first transmissionbeam, the first UE may infer that the first communications link failed.

According to aspects, when the UE receives the RACH message from thesecond UE, the first UE may then transmit a sidelink RACH responsemessage to the second UE, responding to the sidelink RACH messagereceived from the UE and reestablish the first communications linkbetween the first UE and the second UE based, at least in part, on thesidelink RACH response message.

In some cases, in response to detecting that the first communicationslink between the first UE and the second UE has failed (e.g., in somecases, based on not receiving an acknowledgement to a beam failuredetection reference signal), the first UE may remain in the awake stateof the sidelink DRX mode. During the awake state of the sidelink DRXmode, the first UE may perform a sidelink beam failure recoveryprocedure to reestablish the first communications link between the firstUE and the second UE. For example, in some cases, performing thesidelink beam failure recovery procedure may comprise transmitting oneor more sidelink SSBs. In some cases, the first UE may transmit the oneor more sidelink SSBs using multiple different transmission beams.

Thereafter, the first UE may receive, based on the one or more sidelinkSSBs, a sidelink random access channel (RACH) message from the secondUE. In some cases, the sidelink RACH message may include an indicationof at least one transmission beam of the multiple different transmissionbeams used to transmit the one or more sidelink SSBs. Accordingly, thefirst UE may then transmit a sidelink RACH response message to thesecond UE, responding to the sidelink RACH message received from thesecond UE and reestablish the first communications link between thefirst UE and the second UE based, at least in part, on the sidelink RACHresponse message. In some cases, the first communications link may bereestablished using the transmission beam indicated in the RACH message.

Additionally, while the first UE and second UE may communicate using afirst communications link (e.g., sidelink) according to the standaloneresource allocation mode in which the UEs autonomously select sidelinkresources for communication without the assistance of a base station,the first UE may also communicate with the base station using a secondcommunications link between the UE and a base station, such as an accesslink (e.g., Uu communications link). In some cases, the UE may operatein a second DRX mode associated with the second communications link(e.g., the access communications link), such as an access DRX mode. Insome cases, the access DRX mode may be synchronized with the sidelinkDRX mode. Accordingly, during the sidelink beam failure recoveryprocedure, the first UE may remain in an awake state of the access DRXmode. In this case, since the first UE is in the awake state of theaccess DRX mode, the first UE may desire to take advantage of the awakestate and receive control/data signals from the base station during theawake state of the access DRX mode on the second communications link.However, the base station may not know that the first UE is in the awakestate of the access DRX mode since the first UE autonomously handles thesidelink beam failure recovery procedure.

Accordingly, if the first UE desires to communicate (e.g., transmit orreceive) signaling (e.g. control or data signaling) with the basestation, the first UE may further transmit signaling to the base stationindicating that the first UE is in the awake state of the access DRXmode. As noted, the awake state of the access DRX mode may occur at aperiod of time during which the first UE is scheduled to be in a sleepstate of the access DRX mode. However, the first UE may, nevertheless,be in the awake state of the access DRX mode during the period of timewhich the first UE is scheduled to be in the sleep state of the accessDRX mode based on the sidelink beam failure recovery procedure.Accordingly, by transmitting signaling to the base station indicatingthat the first UE is in the awake state of the access DRX mode, thefirst UE may receive at least one data (or control) transmission fromthe BS on the second communications link in response to the signalingindicating that the first UE is in the awake state of the access DRXmode.

In some cases, the first UE may transmit the signaling to the basestation indicating that the first UE is in the awake state of the accessDRX mode after the first communications link between the first UE andthe second UE has been reestablished. In other cases, the first UE maytransmit the signaling to the base station indicating that the first UEis in the awake state of the access DRX mode before the firstcommunications link between the first UE and the second UE has beenreestablished.

Aspects of the present disclosure will now describe techniques performedby the second UE. The techniques described below by the second UE may becomplimentary to the techniques described above with respect to thefirst UE.

For example, FIG. 8 is a flow diagram illustrating example operations800 for wireless communication for sidelink DRX and standalone sidelinkbeam failure detection and recovery, in accordance with certain aspectsof the present disclosure. The operations 800 may be performed, forexample, by a second SL device (e.g., the UE 120 a and/or the UE 120 bin the wireless communication network 100). As noted, operations 800 maybe considered complimentary to operations 700 and may be implemented assoftware components that are executed and run on one or more processors(e.g., controller/processor 280 of FIG. 2). Further, the transmissionand reception of signals by the apparatus in operations 800 may beenabled, for example, by one or more antennas (e.g., antennas 252 ofFIG. 2). In certain aspects, the transmission and/or reception ofsignals by the apparatus may be implemented via a bus interface of oneor more processors (e.g., controller/processor 280) obtaining and/oroutputting signals.

The operations 800 may begin, at 802, by communicating, during an awakestate of a sidelink discontinuous reception (DRX) mode, with a first UEon a first communications link between the first UE and the second UE,wherein a periodicity of the awake state of the sidelink DRX mode isbased on a periodicity for receiving a plurality of beam failuredetection reference signals associated with the first communicationslink.

At 804, the second SL device monitors, during the awake state of thesidelink DRX mode, for the plurality of beam failure detection referencesignals according to the periodicity for receiving the plurality of beamfailure detection reference signals.

According to aspects, the second UE may monitor for the at least onebeam failure detection reference signal in resources configured fortransmitting beam failure detection reference signals, which maycoincide with the awake state of the sidelink DRX mode, as describedabove. For example, in some cases, the second UE may receive, from thefirst UE, at least one beam failure detection reference signal of theplurality of beam failure detection reference signals based on themonitoring. According to aspects, the at least one beam failuredetection reference signal may be received in the awake state of thesidelink DRX mode in resources configured for transmitting beam failuredetection reference signals. Thereafter, the second UE may transmit aresponse message to the first UE, responding to the at least one beamfailure detection reference signal. In this case, since the second UEwas able to receive the at least one beam failure detection signal fromthe first UE, the first communications link has not failed.

In other cases, the second UE may detect that the first communicationslink between the first UE and the second UE has failed based on themonitoring (e.g., based on the second UE not receiving the at least onebeam failure detection signal from the first UE) and may perform a beamfailure recovery procedure to reestablish the first communications linkbetween the first UE and the second UE. As with the first UE, the secondUE may remain in an awake state of the sidelink DRX mode during the beamfailure recovery procedure.

In some cases, performing the beam failure recovery procedure mayinclude receiving one or more sidelink synchronization signal blocks(SSBs) from the first UE based on the detection that the firstcommunications link between the first UE and the second UE has failed.Thereafter, the second UE may transmit a sidelink random access channel(RACH) message to the first UE in response to the received one or moresidelink SSBs. In some cases, as noted above, the RACH message mayinclude an indication of a transmission beam used by the first UE totransmit the one or more sidelink SSBs. Thereafter, the second UE mayreceive a sidelink RACH response message from the first UE based on thesidelink RACH message transmitted to the first UE and may reestablishthe first communications link between the first UE and the second UEbased on the sidelink RACH response message. In some cases, the firstcommunications link may be reestablished using the transmission beamindicated in the RACH message.

Additionally, as with the first UE, since during the beam failurerecovery procedure the second UE remains in an awake state of an accessDRX mode associated with a second communications link between the secondUE and a BS, the second UE may take advantage of the awake state of theaccess DRX mode by communicating with the BS during the awake state ofthe access DRX mode. For example, in some cases, the second UE maytransmit signaling to the BS indicating that the second UE is in theawake state of the access DRX mode. As noted, the awake state of theaccess DRX mode may occur at a period of time during which the second UEis scheduled to be in a sleep state of the access DRX mode. However, thesecond UE may, nevertheless, be in the awake state of the access DRXmode during the period of time which the second UE is scheduled to be inthe sleep state of the access DRX mode based on the sidelink beamfailure recovery procedure. Accordingly, by transmitting signaling tothe base station indicating that the second UE is in the awake state ofthe access DRX mode, the second UE may receive at least one data (orcontrol) transmission from the BS on the second communications link inresponse to the signaling indicating that the first UE is in the accessawake state.

In some cases, the second UE may transmit the signaling to the basestation indicating that the second UE is in the awake state of theaccess DRX mode after the first communications link between the first UEand the second UE has been reestablished. In other cases, the second UEmay transmit the signaling to the base station indicating that thesecond UE is in the awake state of the access DRX mode before the firstcommunications link between the first UE and the second UE has beenreestablished.

Example Wireless Communication Devices

FIG. 9 depicts an example communications device 900 that includesvarious components operable, configured, or adapted to performoperations for the techniques disclosed herein, such as the operationsdepicted and described with respect to FIG. 7. In some examples,communication device 900 may be a user equipment 120 a, 202, 452, 502 asdescribed, for example with respect to FIGS. 1, 2, 4, and 5.

Communications device 900 includes a processing system 902 coupled to atransceiver 908 (e.g., a transmitter and/or a receiver). Transceiver 908is configured to transmit (or send) and receive signals for thecommunications device 900 via an antenna 910, such as the varioussignals as described herein. Processing system 902 may be configured toperform processing functions for communications device 900, includingprocessing signals received and/or to be transmitted by communicationsdevice 900.

Processing system 902 includes one or more processors 920 coupled to acomputer-readable medium/memory 930 via a bus 906. In certain aspects,computer-readable medium/memory 930 is configured to store instructions(e.g., computer-executable code) that when executed by the one or moreprocessors 920, cause the one or more processors 920 to perform theoperations illustrated in FIG. 7, or other operations for performing thevarious techniques discussed herein for sidelink DRX and standalonesidelink beam failure detection and recovery.

In the depicted example, computer-readable medium/memory 930 stores code931 for communicating, code 932 for transmitting, code 933 fordetecting, code 934 for receiving, code 935 for reestablishing, code 936for performing, code 937 for determining, and code 938 for adjusting.

In the depicted example, the one or more processors 920 includecircuitry configured to implement the code stored in thecomputer-readable medium/memory 930, including circuitry 921 forcommunicating, circuitry 922 for transmitting, circuitry 923 fordetecting, circuitry 924 for receiving, circuitry 925 forreestablishing, circuitry 926 for performing, circuitry 927 fordetermining, and circuitry 928 for adjusting.

Various components of communications device 900 may provide means forperforming the methods described herein, including with respect to FIG.7.

In some examples, means for transmitting or sending (or means foroutputting for transmission), as well as means for communicating, mayinclude the transceivers 254 and/or antenna(s) 252 of the user equipment104 illustrated in FIG. 2 and/or transceiver 908 and antenna 910 of thecommunication device 900 in FIG. 9.

In some examples, means for receiving (or means for obtaining), as wellas means for communicating, may include the transceivers 254 and/orantenna(s) 252 of the user equipment 202 illustrated in FIG. 2 and/ortransceiver 908 and antenna 910 of the communication device 900 in FIG.9.

In some examples, means for detecting, means for determining, means forreestablishing, means for performing, and means for adjusting mayinclude various processing system components, such as: the one or moreprocessors 920 in FIG. 9, or aspects of the user equipment 202 depictedin FIG. 2, including receive processor 258, transmit processor 264, TXMIMO processor 266, and/or controller/processor 280 (including sidelinkBFR module 281).

Notably, FIG. 9 is just one example, and many other examples andconfigurations of communication device 900 are possible

FIG. 10 depicts an example communications device 1000 that includesvarious components operable, configured, or adapted to performoperations for the techniques disclosed herein, such as the operationsdepicted and described with respect to FIG. 8. In some examples,communication device 1000 may be a user equipment 120 a, 202, 454, 504as described, for example with respect to FIGS. 1, 2, 4, and 5.

Communications device 1000 includes a processing system 1002 coupled toa transceiver 1008 (e.g., a transmitter and/or a receiver). Transceiver1008 is configured to transmit (or send) and receive signals for thecommunications device 1000 via an antenna 1010, such as the varioussignals as described herein. Processing system 1002 may be configured toperform processing functions for communications device 1000, includingprocessing signals received and/or to be transmitted by communicationsdevice 1000.

Processing system 1002 includes one or more processors 1020 coupled to acomputer-readable medium/memory 1030 via a bus 1006. In certain aspects,computer-readable medium/memory 1030 is configured to store instructions(e.g., computer-executable code) that when executed by the one or moreprocessors 1020, cause the one or more processors 1020 to perform theoperations illustrated in FIG. 8, or other operations for performing thevarious techniques discussed herein for sidelink DRX and standalonesidelink beam failure detection and recovery.

In the depicted example, computer-readable medium/memory 1030 storescode 1031 for communicating, code 1032 for monitoring, code 1033 forreceiving, code 1034 for transmitting, code 1035 for detecting, code1036 for performing, code 1037 for reestablishing, code 1038 fordetermining, and code 1039 for adjusting.

In the depicted example, the one or more processors 1020 includecircuitry configured to implement the code stored in thecomputer-readable medium/memory 1030, including circuitry 1021 forcommunicating, circuitry 1022 for monitoring, circuitry 1023 forreceiving, circuitry 1024 for transmitting, circuitry 1025 fordetecting, circuitry 1026 for performing, circuitry 1027 forreestablishing, circuitry 1028 for determining, and circuitry 1029 foradjusting.

Various components of communications device 1000 may provide means forperforming the methods described herein, including with respect to FIG.8.

In some examples, means for transmitting, means for communicating, orsending (or means for outputting for transmission) may include thetransceivers 254 and/or antenna(s) 252 of the user equipment 104illustrated in FIG. 2 and/or transceiver 1008 and antenna 1010 of thecommunication device 1000 in FIG. 10.

In some examples, means for receiving (or means for obtaining), as wellas means for communicating, may include the transceivers 254 and/orantenna(s) 252 of the user equipment 104 illustrated in FIG. 2 and/ortransceiver 1008 and antenna 1010 of the communication device 1000 inFIG. 10.

In some examples, means for performing, means for reestablishing, andmeans for monitoring, means for detecting, means for adjusting, andmeans for determining may include various processing system components,such as: the one or more processors 1020 in FIG. 10, or aspects of theuser equipment 104 depicted in FIG. 2, including receive processor 258,transmit processor 264, TX MIMO processor 266, and/orcontroller/processor 280 (including sidelink BFR module 281).

Notably, FIG. 10 is just one example, and many other examples andconfigurations of communication device 1000 are possible.

Example Clauses

Implementation examples are described in the following numbered clauses:

Clause 1: A method for wireless communication performed by a first userequipment (UE), comprising: communicating, while operating in a sidelinkdiscontinuous reception (DRX) mode, with a second UE on a firstcommunications link between the first UE and the second UE;transmitting, during an awake state of the sidelink DRX mode, at leastone beam failure detection reference signal of a plurality of beamfailure detection reference signals associated with the firstcommunications link, wherein a periodicity of the awake state of thesidelink DRX mode is based on a periodicity for transmitting theplurality of beam failure detection reference signals; and detectingthat the first communications link between the first UE and the secondUE has failed based on the at least one beam failure detection referencesignal.

Clause 2: The method of Clause 1, wherein the plurality of beam failuredetection reference signals comprise at least one of: sidelink channelstate information reference signals (CSI-RSs); or sidelinksynchronization signal blocks (SSBs).

Clause 3: The method of any one of Clauses 1-2, wherein detecting thatthe first communications link between the first UE and the second UE hasfailed based on the at least one beam failure detection reference signalcomprises: not receiving, within a threshold period of time, a responsemessage from the second UE, responding to the at least one beam failuredetection reference signal; and detecting that the first communicationslink between the first UE and the second UE has failed is further basedon not receiving the response message from the second UE within thethreshold period of time.

Clause 4: The method of any one of Clauses 1-2, wherein detecting thatthe first communications link between the first UE and the second UE hasfailed based on the at least one beam failure detection reference signalcomprises: receiving a sidelink random access channel (RACH) messagefrom the second UE in response to the at least one beam failuredetection reference signal; and detecting that the first communicationslink between the first UE and the second UE has failed is further basedon the sidelink RACH message received from the second UE.

Clause 5: The method of Clause 4, wherein the sidelink RACH messageindicates a transmission beam different from that associated with thefirst communications link.

Clause 6: The method of any one of Clauses 4-5, wherein the at one beamfailure detection reference signal comprises at least one sidelinksynchronization signal block (SSB).

Clause 7: The method of claim any one of Clauses 4-5, furthercomprising: transmitting a sidelink RACH response message to the secondUE, responding to the sidelink RACH message received from the UE; andreestablishing the first communications link between the first UE andthe second UE based, at least in part, on the sidelink RACH responsemessage.

Clause 8: The method of any one of Clauses 1-7, further comprisingremaining in the awake state of the sidelink DRX mode in response todetecting that the first communications link between the first UE andthe second UE has failed.

Clause 9: The method of Clause 8, further comprising performing, duringthe awake state of the sidelink DRX mode, a sidelink beam failurerecovery procedure to reestablish the first communications link betweenthe first UE and the second UE.

Clause 10: The method of Clause 9, wherein performing the sidelink beamfailure recovery procedure comprises: transmitting one or more sidelinksynchronization signal blocks (SSBs); receiving, based on the one ormore sidelink SSBs, a sidelink random access channel (RACH) message fromthe second UE; transmitting a sidelink RACH response message to thesecond UE, responding to the sidelink RACH message received from thesecond UE; and reestablishing the first communications link between thefirst UE and the second UE based, at least in part, on the sidelink RACHresponse message.

Clause 11: The method of Clause 10, wherein: transmitting the one ormore sidelink SSBs comprises transmitting the one or more sidelink SSBsusing multiple different transmission beams; and the sidelink RACHmessage includes an indication of at least one transmission beam of themultiple different transmission beams.

Clause 12: The method of any one of Clauses 10-11, further comprising:communicating with a base station (BS) on a second communications linkbetween the first UE and the BS; transmitting signaling to the BSindicating that the first UE is in an awake state of an access DRX modeassociated with the second communications link; and receiving at leastone data transmission from the BS in response to the signalingindicating that the first UE is in the awake state of the access DRXmode associated with the second communications link.

Clause 13: The method of Clause 12, wherein: the awake state of theaccess DRX mode occurs at a period of time during which the first UE isscheduled to be in a sleep state of the access DRX mode; and the UE isin the awake state of the access DRX mode during the period of timewhich the first UE is scheduled to be in the sleep state of the accessDRX mode based on the sidelink beam failure recovery procedure.

Clause 14: The method of any one of Clauses 12-13, wherein transmittingthe signaling to the BS indicating that the first UE is in the awakestate of the access DRX mode comprises transmitting the signaling to thebase station indicating that the first UE is in the awake state of theaccess DRX mode after the first communications link between the first UEand the second UE has been reestablished.

Clause 15: The method of any one of Clauses 1-14, wherein the firstcommunications link comprises a sidelink between the first UE and thesecond UE.

Clause 16: The method of any one of Clauses 1-15, further comprising:determining a change in the periodicity for transmitting the pluralityof beam failure detection reference signals; and adjusting at least oneof the periodicity of the awake state of the sidelink DRX mode or aperiodicity of a sleep state of the sidelink DRX mode based on thedetermined change in the periodicity for transmitting the plurality ofbeam failure detection reference signals.

Clause 17: The method of Clause 16, wherein: the determined changeincreases the periodicity for transmitting the plurality of beam failuredetection reference signals; and adjusting at least one of theperiodicity of the awake state of the sidelink DRX mode or theperiodicity of the sleep state of the sidelink DRX mode comprises atleast one of increasing the periodicity of the awake state of thesidelink DRX mode or increasing the periodicity of the sleep state ofthe sidelink DRX mode.

Clause 18: The method of Clause 16, wherein: the determined changedecreases the periodicity for transmitting the plurality of beam failuredetection reference signals; and adjusting at least one of theperiodicity of the awake state of the sidelink DRX mode or theperiodicity of the sleep state of the sidelink DRX mode comprises atleast one of decreasing the periodicity of the awake state of thesidelink DRX mode or decreasing the periodicity of the sleep state ofthe sidelink DRX mode.

Clause 19: A method for wireless communication performed by a seconduser equipment (UE), comprising: communicating, during an awake state ofa sidelink discontinuous reception (DRX) mode, with a first UE on afirst communications link between the first UE and the second UE,wherein a periodicity of the awake state of the sidelink DRX mode isbased on a periodicity for receiving a plurality of beam failuredetection reference signals associated with the first communicationslink; and monitoring, during the awake state of the sidelink DRX mode,for the plurality of beam failure detection reference signals accordingto the periodicity for receiving the plurality of beam failure detectionreference signals.

Clause 20: The method of Clause 19, further comprising: receiving, fromthe first UE, at least one beam failure detection reference signal ofthe plurality of beam failure detection reference signals based on themonitoring; and transmitting a response message to the first UE,responding to the at least one beam failure detection reference signal.

Clause 21: The method of any one of Clauses 19-20, further comprising:detecting that the first communications link between the first UE andthe second UE has failed based on the monitoring; and performing asidelink beam failure recovery procedure to reestablish the firstcommunications link between the first UE and the second UE.

Clause 22: The method of Clause 21, wherein performing the sidelink beamfailure recovery procedure comprises remaining in the awake state of thesidelink DRX mode.

Clause 23: The method of Clause 22, wherein performing the sidelink beamfailure recovery procedure further comprises: receiving one or moresidelink synchronization signal blocks (SSBs) from the first UE based onthe detection that the first communications link between the first UEand the second UE has failed; and transmitting a sidelink random accesschannel (RACH) message to the first UE in response to the received oneor more sidelink SSBs.

Clause 24: The method of Clause 23, wherein performing the sidelink beamfailure recovery procedure further comprises: receiving a sidelink RACHresponse message from the first UE based on the sidelink RACH messagetransmitted to the first UE; and reestablishing the first communicationslink between the first UE and the second UE based on the sidelink RACHresponse message.

Clause 25: The method of Clause 24, further comprising: communicatingwith a base station (BS) on a second communications link between thesecond UE and the BS; transmitting signaling to the BS indicating thatthe second UE is in an awake state of an access DRX mode associated withthe second communications link; and receiving at least one datatransmission from the BS in response to the signaling indicating thatthe second UE is in the awake state of the access DRX mode associatedwith the second communications link.

Clause 26: The method of Clause 25, wherein: the awake state of theaccess DRX mode occurs at a period of time during which the second UE isscheduled to be in a sleep state of the access DRX mode; and the secondUE is in the awake state of the access DRX mode during the period oftime which the second UE is scheduled to be in the sleep state of theaccess DRX mode based on the sidelink beam failure recovery procedure.

Clause 27: The method of any one of Clauses 25-26, wherein transmittingthe signaling to the BS indicating that the second UE is in the awakestate of the access DRX mode comprises transmitting the signaling to theBS indicating that the second UE is in the awake state of the access DRXmode after the first communications link between the first UE and thesecond UE has been reestablished.

Clause 28: The method of any one of Clauses 19-27, wherein the firstcommunications link comprises a sidelink between the first UE and thesecond UE.

Clause 29: The method of any one of Clauses 19-28, further comprising:determining a change in the periodicity for transmitting the pluralityof beam failure detection reference signals; and adjusting at least oneof the periodicity of the awake state of the sidelink DRX mode or aperiodicity of a sleep state of the sidelink DRX mode based on thedetermined change in the periodicity for transmitting the plurality ofbeam failure detection reference signals.

Clause 30: The method of Clause 29, wherein: the determined changeincreases the periodicity for transmitting the plurality of beam failuredetection reference signals; and adjusting at least one of theperiodicity of the awake state of the sidelink DRX mode or theperiodicity of the sleep state of the sidelink DRX mode comprises atleast one of increasing the periodicity of the awake state of thesidelink DRX mode or increasing the periodicity of the sleep state ofthe sidelink DRX mode.

Clause 31: The method of Clause 29, wherein: the determined changedecreases the periodicity for transmitting the plurality of beam failuredetection reference signals; and adjusting at least one of theperiodicity of the awake state of the sidelink DRX mode or theperiodicity of the sleep state of the sidelink DRX mode comprises atleast one of decreasing the periodicity of the awake state of thesidelink DRX mode or decreasing the periodicity of the sleep state ofthe sidelink DRX mode.

Clause 32: An apparatus for wireless communication, comprising: a memorycomprising executable instructions; and one or more processorsconfigured to execute the executable instructions and cause theapparatus to perform a method in accordance with any one of Clauses1-31.

Clause 33: An apparatus for wireless communication, comprising means forperforming a method in accordance with any one of Clauses 1-31.

Clause 34: A non-transitory computer-readable medium for wirelesscommunication comprising executable instructions that, when executed byone or more processors of an apparatus, cause the apparatus to perform amethod in accordance with any one of Clauses 1-31.

Clause 35: A computer program product for wireless communicationembodied on a computer-readable storage medium comprising code forperforming a method in accordance with any one of Clauses 1-31.

Additional Considerations

The techniques described herein may be used for various wirelesscommunication technologies, such as NR (e.g., 5G NR), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDMA), single-carrier frequency division multiple access (SC-FDMA),time division synchronous code division multiple access (TD-SCDMA), andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). LTEand LTE-A are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE,LTE-A and GSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). cdma2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). NR is an emerging wireless communications technologyunder development.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB)and/or a NB subsystem serving this coverage area, depending on thecontext in which the term is used. In NR systems, the term “cell” andBS, next generation NodeB (gNB or gNodeB), access point (AP),distributed unit (DU), carrier, or transmission reception point (TRP)may be used interchangeably. A BS may provide communication coverage fora macro cell, a pico cell, a femto cell, and/or other types of cells. Amacro cell may cover a relatively large geographic area (e.g., severalkilometers in radius) and may allow unrestricted access by UEs withservice subscription. A pico cell may cover a relatively smallgeographic area and may allow unrestricted access by UEs with servicesubscription. A femto cell may cover a relatively small geographic area(e.g., a home) and may allow restricted access by UEs having anassociation with the femto cell (e.g., UEs in a Closed Subscriber Group(CSG), UEs for users in the home, etc.). A BS for a macro cell may bereferred to as a macro BS. A BS for a pico cell may be referred to as apico BS. A BS for a femto cell may be referred to as a femto BS or ahome BS.

A UE may also be referred to as a mobile station, a terminal, an accessterminal, a subscriber unit, a station, a Customer Premises Equipment(CPE), a cellular phone, a smart phone, a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a laptop computer, a cordless phone, a wireless local loop (WLL)station, a tablet computer, a camera, a gaming device, a netbook, asmartbook, an ultrabook, an appliance, a medical device or medicalequipment, a biometric sensor/device, a wearable device such as a smartwatch, smart clothing, smart glasses, a smart wrist band, smart jewelry(e.g., a smart ring, a smart bracelet, etc.), an entertainment device(e.g., a music device, a video device, a satellite radio, etc.), avehicular component or sensor, a smart meter/sensor, industrialmanufacturing equipment, a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. Some UEs may be considered machine-type communication(MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include,for example, robots, drones, remote devices, sensors, meters, monitors,location tags, etc., that may communicate with a BS, another device(e.g., remote device), or some other entity. A wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as Internet or a cellular network) via a wired orwireless communication link. Some UEs may be consideredInternet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT)devices.

In some examples, access to the air interface may be scheduled. Ascheduling entity (e.g., a BS) allocates resources for communicationamong some or all devices and equipment within its service area or cell.The scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. In someexamples, a UE may function as a scheduling entity and may scheduleresources for one or more subordinate entities (e.g., one or more otherUEs), and the other UEs may utilize the resources scheduled by the UEfor wireless communication. In some examples, a UE may function as ascheduling entity in a peer-to-peer (P2P) network, and/or in a meshnetwork. In a mesh network example, UEs may communicate directly withone another in addition to communicating with a scheduling entity.

The methods disclosed herein comprise one or more steps or actions forachieving the methods. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112(f) unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal (see FIG. 1), a user interface (e.g., keypad, display, mouse,joystick, etc.) may also be connected to the bus. The bus may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, power management circuits, and the like, which are wellknown in the art, and therefore, will not be described any further. Theprocessor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein, for example, instructions for performing the operationsdescribed herein and illustrated in FIG. 7 and/or FIG. 8 as well asother operations described herein for sidelink DRX and standalonesidelink beam failure detection and recovery.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

1. A method for wireless communication performed by a first userequipment (UE), comprising: communicating, while operating in a sidelinkdiscontinuous reception (DRX) mode, with a second UE on a firstcommunications link between the first UE and the second UE, wherein thefirst communications link comprises a sidelink between the first UE andthe second UE; transmitting, during an awake state of the sidelink DRXmode, at least one beam failure detection reference signal of aplurality of beam failure detection reference signals associated withthe first communications link, wherein a periodicity of the awake stateof the sidelink DRX mode is based on a periodicity for transmitting theplurality of beam failure detection reference signals; and detectingthat the first communications link between the first UE and the secondUE has failed based on the at least one beam failure detection referencesignal.
 2. The method of claim 1, further comprising: remaining in theawake state of the sidelink DRX mode in response to detecting that thefirst communications link between the first UE and the second UE hasfailed; and performing, during the awake state of the sidelink DRX mode,a sidelink beam failure recovery procedure to reestablish the firstcommunications link between the first UE and the second UE.
 3. Themethod of claim 2, wherein performing the sidelink beam failure recoveryprocedure comprises: transmitting one or more sidelink synchronizationsignal blocks (SSBs); receiving, based on the one or more sidelink SSBs,a sidelink random access channel (RACH) message from the second UE;transmitting a sidelink RACH response message to the second UE,responding to the sidelink RACH message received from the second UE; andreestablishing the first communications link between the first UE andthe second UE based, at least in part, on the sidelink RACH responsemessage.
 4. The method of claim 3, wherein: transmitting the one or moresidelink SSBs comprises transmitting the one or more sidelink SSBs usingmultiple different transmission beams; and the sidelink RACH messageincludes an indication of at least one transmission beam of the multipledifferent transmission beams.
 5. The method of claim 3, furthercomprising: communicating with a base station (BS) on a secondcommunications link between the first UE and the BS; transmittingsignaling to the BS indicating that the first UE is in an awake state ofan access DRX mode associated with the second communications link; andreceiving at least one data transmission from the BS in response to thesignaling indicating that the first UE is in the awake state of theaccess DRX mode associated with the second communications link.
 6. Themethod of claim 5, wherein: the awake state of the access DRX modeoccurs at a period of time during which the first UE is scheduled to bein a sleep state of the access DRX mode; and the UE is in the awakestate of the access DRX mode during the period of time which the firstUE is scheduled to be in the sleep state of the access DRX mode based onthe sidelink beam failure recovery procedure.
 7. The method of claim 5,wherein transmitting the signaling to the BS indicating that the firstUE is in the awake state of the access DRX mode comprises transmittingthe signaling to the base station indicating that the first UE is in theawake state of the access DRX mode after the first communications linkbetween the first UE and the second UE has been reestablished.
 8. Themethod of claim 1, wherein the plurality of beam failure detectionreference signals comprise at least one of: sidelink channel stateinformation reference signals (CSI-RSs); or sidelink synchronizationsignal blocks (SSBs).
 9. The method of claim 1, wherein detecting thatthe first communications link between the first UE and the second UE hasfailed based on the at least one beam failure detection reference signalcomprises: not receiving, within a threshold period of time, a responsemessage from the second UE, responding to the at least one beam failuredetection reference signal; and detecting that the first communicationslink between the first UE and the second UE has failed is further basedon not receiving the response message from the second UE within thethreshold period of time.
 10. The method of claim 1, wherein detectingthat the first communications link between the first UE and the secondUE has failed based on the at least one beam failure detection referencesignal comprises: receiving a sidelink random access channel (RACH)message from the second UE in response to the at least one beam failuredetection reference signal; and detecting that the first communicationslink between the first UE and the second UE has failed is further basedon the sidelink RACH message received from the second UE.
 11. The methodof claim 10, wherein the sidelink RACH message indicates a transmissionbeam different from that associated with the first communications link.12. The method of claim 10, wherein the at one beam failure detectionreference signal comprises at least one sidelink synchronization signalblock (SSB).
 13. The method of claim 10, further comprising:transmitting a sidelink RACH response message to the second UE,responding to the sidelink RACH message received from the UE; andreestablishing the first communications link between the first UE andthe second UE based, at least in part, on the sidelink RACH responsemessage.
 14. The method of claim 1, further comprising: determining achange in the periodicity for transmitting the plurality of beam failuredetection reference signals; and adjusting at least one of theperiodicity of the awake state of the sidelink DRX mode or a periodicityof a sleep state of the sidelink DRX mode based on the determined changein the periodicity for transmitting the plurality of beam failuredetection reference signals.
 15. The method of claim 14, wherein: thedetermined change increases the periodicity for transmitting theplurality of beam failure detection reference signals; and adjusting atleast one of the periodicity of the awake state of the sidelink DRX modeor the periodicity of the sleep state of the sidelink DRX mode comprisesat least one of increasing the periodicity of the awake state of thesidelink DRX mode or increasing the periodicity of the sleep state ofthe sidelink DRX mode.
 16. The method of claim 14, wherein: thedetermined change decreases the periodicity for transmitting theplurality of beam failure detection reference signals; and adjusting atleast one of the periodicity of the awake state of the sidelink DRX modeor the periodicity of the sleep state of the sidelink DRX mode comprisesat least one of decreasing the periodicity of the awake state of thesidelink DRX mode or decreasing the periodicity of the sleep state ofthe sidelink DRX mode.
 17. A method for wireless communication performedby a second user equipment (UE), comprising: communicating, during anawake state of a sidelink discontinuous reception (DRX) mode, with afirst UE on a first communications link between the first UE and thesecond UE, wherein a periodicity of the awake state of the sidelink DRXmode is based on a periodicity for receiving a plurality of beam failuredetection reference signals associated with the first communicationslink, wherein the first communications link comprises a sidelink betweenthe first UE and the second UE; and monitoring, during the awake stateof the sidelink DRX mode, for the plurality of beam failure detectionreference signals according to the periodicity for receiving theplurality of beam failure detection reference signals.
 18. The method ofclaim 17, further comprising: receiving, from the first UE, at least onebeam failure detection reference signal of the plurality of beam failuredetection reference signals based on the monitoring; and transmitting aresponse message to the first UE, responding to the at least one beamfailure detection reference signal.
 19. The method of claim 17, furthercomprising: detecting that the first communications link between thefirst UE and the second UE has failed based on the monitoring; andperforming a sidelink beam failure recovery procedure to reestablish thefirst communications link between the first UE and the second UE. 20.The method of claim 19, wherein performing the sidelink beam failurerecovery procedure comprises remaining in the awake state of thesidelink DRX mode.
 21. The method of claim 20, wherein performing thesidelink beam failure recovery procedure further comprises: receivingone or more sidelink synchronization signal blocks (SSBs) from the firstUE based on the detection that the first communications link between thefirst UE and the second UE has failed; and transmitting a sidelinkrandom access channel (RACH) message to the first UE in response to thereceived one or more sidelink SSBs.
 22. The method of claim 21, whereinperforming the sidelink beam failure recovery procedure furthercomprises: receiving a sidelink RACH response message from the first UEbased on the sidelink RACH message transmitted to the first UE; andreestablishing the first communications link between the first UE andthe second UE based on the sidelink RACH response message.
 23. Themethod of claim 22, further comprising: communicating with a basestation (BS) on a second communications link between the second UE andthe BS; transmitting signaling to the BS indicating that the second UEis in an awake state of an access DRX mode associated with the secondcommunications link; and receiving at least one data transmission fromthe BS in response to the signaling indicating that the second UE is inthe awake state of the access DRX mode associated with the secondcommunications link.
 24. The method of claim 23, wherein: the awakestate of the access DRX mode occurs at a period of time during which thesecond UE is scheduled to be in a sleep state of the access DRX mode;and the second UE is in the awake state of the access DRX mode duringthe period of time which the second UE is scheduled to be in the sleepstate of the access DRX mode based on the sidelink beam failure recoveryprocedure.
 25. The method of claim 23, wherein transmitting thesignaling to the BS indicating that the second UE is in the awake stateof the access DRX mode comprises transmitting the signaling to the BSindicating that the second UE is in the awake state of the access DRXmode after the first communications link between the first UE and thesecond UE has been reestablished.
 26. The method of claim 17, furthercomprising: determining a change in the periodicity for transmitting theplurality of beam failure detection reference signals; and adjusting atleast one of the periodicity of the awake state of the sidelink DRX modeor a periodicity of a sleep state of the sidelink DRX mode based on thedetermined change in the periodicity for transmitting the plurality ofbeam failure detection reference signals.
 27. The method of claim 26,wherein: the determined change increases the periodicity fortransmitting the plurality of beam failure detection reference signals;and adjusting at least one of the periodicity of the awake state of thesidelink DRX mode or the periodicity of the sleep state of the sidelinkDRX mode comprises at least one of increasing the periodicity of theawake state of the sidelink DRX mode or increasing the periodicity ofthe sleep state of the sidelink DRX mode.
 28. The method of claim 26,wherein: the determined change decreases the periodicity fortransmitting the plurality of beam failure detection reference signals;and adjusting at least one of the periodicity of the awake state of thesidelink DRX mode or the periodicity of the sleep state of the sidelinkDRX mode comprises at least one of decreasing the periodicity of theawake state of the sidelink DRX mode or decreasing the periodicity ofthe sleep state of the sidelink DRX mode.
 29. An apparatus for wirelesscommunication by a first user equipment (UE), comprising: a memorycomprising executable instructions; and one or more processorsconfigured to execute the executable instructions and cause theapparatus to: communicate, while operating in a sidelink discontinuousreception (DRX) mode, with a second UE on a first communications linkbetween the first UE and the second UE, wherein the first communicationslink comprises a sidelink between the first UE and the second UE;transmit, during an awake state of the sidelink DRX mode, at least onebeam failure detection reference signal of a plurality of beam failuredetection reference signals associated with the first communicationslink, wherein a periodicity of the awake state of the sidelink DRX modeis based on a periodicity for transmitting the plurality of beam failuredetection reference signals; and detect that the first communicationslink between the first UE and the second UE has failed based on the atleast one beam failure detection reference signal.
 30. An apparatus forwireless communication by a second user equipment (UE), comprising: amemory comprising executable instructions; and one or more processorsconfigured to execute the executable instructions and cause theapparatus to: communicate, during an awake state of a sidelinkdiscontinuous reception (DRX) mode, with a first UE on a firstcommunications link between the first UE and the second UE, wherein aperiodicity of the awake state of the sidelink DRX mode is based on aperiodicity for receiving a plurality of beam failure detectionreference signals associated with the first communications link, whereinthe first communications link comprises a sidelink between the first UEand the second UE; and monitor, during the awake state of the sidelinkDRX mode, for the plurality of beam failure detection reference signalsaccording to the periodicity for receiving the plurality of beam failuredetection reference signals.